This invention relates to element monitors and more particularly to a hybrid plasma element monitor utilizing a high voltage electric discharge along with microwave radiation.
There is an increasing need for affordable, high sensitivity and easy to use methods to analyze water and gas samples for contaminants and other metallic content. Currently, water samples are analyzed for metallic content using a traditional inductively coupled plasma (ICP) in a laboratory. With this method, any sediment in the water is digested through acid additives and the solution is then injected into the ICP flame through a nebulizer. The nebulizer aerosolizes the solution into a fine mist. This aerosol is then heated to the vapor stage and subsequently cooled, allowing the water to be condensed out. What is left is the sediment content of the solution that is injected into the plasma for analysis. The limitations of this technique are that in addition to the cost of the ICP devices and ultrasonic nebulizers, this method generates a lot of hazardous waste and the required sample preparation is complicated and samples sizes are greatly restricted. The nebulizer transducer lifetime is limited and its efficiency diminishes with time making it essential to recalibrate the system often. Further, the method can only run in a laboratory environment with special gases such as argon. ICP is therefore unsuitable for field use.
Other methods have been developed for element monitoring but they have not been commercially used for matter analysis. These methods include a microwave generated plasma elements sensor developed at the Massachusetts Institute of Technology. See U.S. Pat. No. 5,909,277. Another similar technology that runs with argon gas was developed at the Los Alamos National Laboratory. See U.S. Pat. No. 6,429,935 The microwave plasma element sensors disclosed in U.S. Pat. No. 5,909,277 and No. 6,429,935 require costly, well regulated power supplies necessary to prevent the plasma from being extinguished by high sample throughput. These microwave plasma element sensors also require a minimum high power level above 500 Watts to sustain the plasma. In addition, these plasmas are difficult to start and therefore can not be pulsed easily to reduce average power requirements. A plasma atomic excitation technology that separates the plasma generation and excitation functions would improve the performance of these plasma element sensors and make possible reductions in required power levels with high sample throughputs.